Internal combustion engines are designed to operate within certain normal operating conditions of temperature and oil pressure. These normal conditions for internal combustion engines require the circulation of oil under pressure to lubricate their working parts and, if such oil pressure is lost, this condition indicates the lack of circulation of oil. Marine engines typically either have circulating air or circulating water to cool them and any failure of the coolant circulation rapidly causes an increase in the temperature of the engine. In addition, outboard marine engines of the two-cycle variety normally mix oil and gasoline for their fuel. A lack of sufficient oil in the fuel mixture for a two-cycle engine can additionally cause an abnormal condition to occur.
Any of these conditions which are not in the normal operating range of the engine can cause extensive damage if not communicated quickly to the operator of the engine. However, the operator, if reasonably alerted to such abnormal condition, can take action to determine their cause and correct them to prevent such damage. There are many types of engine monitoring or warning systems for internal combustion engines which attempt to solve these problems by providing visual or audible annunciations of abnormal conditions. In addition, there are engine monitoring systems which are used particularly for outboard marine engines.
One such monitoring system is illustrated in U.S. patent application Ser. No. 201,085, now allowed, entitled "Single Wire Engine Indicator Device" by R.J. Bragenzer et al., which is commonly assigned with the present application. The disclosure of Bragenzer is hereby expressly incorporated by reference herein.
Another such monitoring system is described in U.S. Pat. No. 4,019,489 entitled "Safety Apparatus for Engines" by Cartmill. Cartmill discloses a circuit that is responsive to water pressure, oil pressure, and engine temperature. Each of these variables is detected by a conventional sensor that is connected by its own insulated wire to an electronic circuit at a remote location.
These and other prior monitoring systems, although being serviceable for their environment, use an external power supply line which is generally termed switched B.sup.+. The switched B.sup.+ power supply line for an outboard engine is the battery voltage connected to a separate line which is switched through the starting key switch and then used for accessories, including any engine monitoring or warning system. The engine is started with the key in the "start" position for cranking and then the key is turned to the "run" position to power the accessories while the engine is operating. However, there are many outboard marine engines which do not have a switched B.sup.+ power supply line and, therefore, cannot take advantage of such warning systems. It would be extremely advantageous to provide an engine warning system for these outboard engines, and other internal combustion engines, which do not include a switched B.sup.+ power supply line.
But, while engine warning systems would be advantageous on these engines, the need for keeping such systems elegant and simple is paramount. Generally, engines without a switched B.sup.+ power line are small displacement engines, such as small outboard marine engines, which are designed for less complexity and few, if any, accessories. To be a viable addition to such engines, the engine warning system cannot overcomplicate the design or require exotic components. Further, such warning systems need to be compact to match the existing small profiles and cowlings of such engines and rugged to survive in the environment such engines are used in.